The 19-year-old lasted just 12 minutes of England's Under-21 friendly defeat to Italy on Tuesday before he was substituted with the injury.
He underwent assessment at the club's Finch Farm training ground on Wednesday and later used Twitter to suggest he would be out for "four to six weeks".
The club's website, evertonfc.com, however, said they expected to be without the teenager for a month.
Source: PA
